Nutrient analyses are a broad need in environmental science, with many agencies engaged in measurement of parameters of analytes, such as, but not limited to, nitrate, ammonium, and phosphate concentrations. These concentrations are critically important for function of aquatic ecosystems, and are then often used as proxies for ecosystem health. As such, agencies with water quality mandates (e.g. regulatory agencies, monitoring agencies), industries operating on discharge permits (e.g. water treatment plants), environmental engineering firms, conservation authorities, and environmental scientists are all generating high volumes of nutrient concentration data.
Currently, concentrations of analytes such as nitrate, ammonium, and phosphate may be measured based on colorimetric reactions. Standard methods for colorimetric analysis of nutrients are well established and remain largely unchanged over the past 3 decades. Other methods for quantification of nutrients include ion chromatography and ion selective electrodes. In general, colorimetric analysis remains the most common mode of nutrient analysis as these methods generally offer greater sensitivity (i.e. lower detection limits) than ion chromatography and, especially, ion selective electrodes. Colorimetric methods are also generally less sensitive to interference by other ions. Finally, colorimetric analysis requires the least specialized equipment and has low barriers for entry by users, specifically the cost and required expertise are low.
Currently, the only field methods for these analyses are test kits that are semi-quantitative and do not generate research quality data. Moreover, the kits are expensive and not amenable to large sampling campaigns. Laboratory-based nutrient analysers that generate research quality data (e.g. Lachat and ion chromatography-based systems) require that samples be preserved in the field and transported to the laboratory, so data are not available immediately. Moreover, these systems are expensive preventing adoption by many potential users.
Colorimetric methods make nutrients a laboratory parameter rather than a field parameter, meaning that these methods require that samples be collected from the field, preserved on site, and processed at a later time in the laboratory. Generally, these methods also require a significant sample size (e.g. 10-50 mL of sample) and generate a commensurate volume of waste. Further, the processing of individual samples is tedious, requiring precise volumes of sample and reagents to be measured and combined for each reaction. Some similar constraints exist for ion chromatography. Samples must be preserved and transported to the laboratory, requiring later processing and generally requiring large volumes.
It would be preferable to perform nutrient analyses using smaller volumes, particularly in situations where only small volumes of sample may be collected.
It would be preferable to generate smaller volumes of waste.
Finally, it would be preferable for nutrient analyses to be a field parameter, measured on site (in the field) without the requirement to preserve and transport samples. Such processing introduces a level of uncertainty into the subsequent quantification of the analyte.